Back-up, or uninterruptable, power supplies have numerous uses in electronics applications to provide a back-up power source to a primary power system, such as AC line power, or a primary battery system. A particular use for such systems is in high end computer applications, such as mainframes, minicomputers, supercomputers, network servers, and the like to prevent data loss during an interruption of the primary power to the computer. For example, the AS/400 minicomputer system manufactured by International Business Machines Corp. includes an internal back-up power supply which is used to provide back-up power and shorten the IPL time after an AC main power failure. One design of an internal back-up power supply useful for the AS/400 minicomputer includes an integrated battery charger, system interface circuit and batteries that are mounted in a single case in an enclosure in the AS/400 system.
Many back-up power supplies include one or more batteries which have only limited lives and must be replaced periodically. For example, the AS/400 computer system uses lead acid batteries that have been found to last about 4 years before needing to be replaced.
However, there are several drawbacks associated with the replacement of the batteries in many conventional back-up power supplies. For example, the batteries used in such systems are typically integrated with the charger and system interface circuitry, and thereby require all the components to be replaced together even though the circuitry may still be operational. Moreover, replacement of batteries in conventional systems is typically performed by calling service personnel due to the substantial labor and expertise required to replace the batteries. In addition, replacement of batteries may require the computer system to be shut down in part or in whole, thereby resulting in some loss of productivity.
All of the above drawbacks result in higher operating costs and greater inconvenience for owners and operators of such systems. Therefore, a substantial need has arisen for a simple-to-maintain back-up power supply which permits used batteries to be replaced by an owner or operator without having to call service personnel, without having to replace all of the charger and other supporting electronic components, and without requiring the system to be shut down.